n biology, regeneration is the process of renewal, restoration, and growth that makes genomes, cells, organs,organisms, and ecosystems resilient to natural fluctuations or events that cause disturbance or damage. Every species is capable of regeneration, from bacteria to humans At its most elementary level, regeneration is mediated by the molecular processes of DNA synthesis.] Regeneration in biology, however, mainly refers to the morphogenic processes that characterizes the phenotypic plasticity of traits allowing multi-cellular organisms to repair and maintain the integrity of their physiological and morphological states. Above the genetic level, regeneration is fundamentally regulated by asexual cellular processes. It is important to note that regeneration is different from reproduction. For example, hydra performs regeneration but it reproduces by the method of budding.
The hydra and the planarian flatworm have long served as model organisms for their highly adaptive regenerative capabilities. Once wounded, their cells become activated and start to remodel tissues and organs back to the pre-existing state. The Caudata ("urodeles"; salamanders and newts), an order of tailed amphibians, is possibly the most adept vertebrate group at regeneration, given their capability of regenerating limbs, tails, jaws, eyes and a variety of internal structures. The regeneration of organs is a common and widespread adaptive capability among metazoan creatures. In a related context, some animals are able to reproduce asexually through fragmentation, budding, or fission. A planarian parent, for example, will constrict, split in the middle, and each half generates a new end to form two clones of the original. Echinoderms (such as the starfish), crayfish, many reptiles, and amphibians exhibit remarkable examples of tissue regeneration. The case of autotomy, for example, serves as a defensive function as the animal detaches a limb or tail to avoid capture. After the limb or tail has been autotomized, cells move into action and tissues regenerate. Ecosystems are regenerative as well. Following a disturbance, such as a fire or pest outbreak in a forest, pioneering species will occupy, compete for space, and establish themselves in the newly opened habitat. The new growth of seedlings and community assembly process is known as regeneration in ecology.